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What is anti-clotting medication and how is it used safely?

Anti-clotting medication is used to prevent blood clots from forming, and therefore lower the risk of certain cardiovascular diseases like heart attacks and strokes. As the name suggests, they make sure that the blood does not clot as quickly. The colloquial term "blood thinner" is not strictly correct, because the medication does not actually thin the blood, but rather make sure that certain components of the blood do not stick together so easily. Anti-clotting medications can be divided into two groups: Anticoagulants stop clotting factors from forming or working. Antiplatelets stop the blood platelets (thrombocytes) from clotting so easily.

What are the most common anticoagulants and how are they used?

The most commonly used anticoagulants in Germany at the moment are coumarins, such as phenprocoumon and warfarin. Coumarin medications are very strong. When people use them it takes a lot longer for their blood to clot. Coumarins are usually taken by people who have a high risk of stroke. They include people with artificial heart valves, atrial fibrillation and people who have had pulmonary embolism. Coumarins are particularly suitable for long-term use because they can be taken as tablets.

Although the strength of the anticoagulant effect does depend on the dose of coumarins, it can also vary greatly from person to person, and even over time in the same person. It is therefore important for the blood's clotting ability to be regularly monitored during treatment.

Pregnant women are usually not allowed to take coumarins because they can be harmful to unborn babies. So it is important that women who are taking coumarins make sure that they use effective contraception and talk to their doctor if they planning to get pregnant. Women should also avoid taking coumarins while they are still breastfeeding. The medication can enter the child's bloodstream via breastmilk and then also stop their blood from clotting.

Phenprocoumon is the most frequently prescribed coumarin in Germany. Many people know it under its trade name marcumar, but it is also available as marcuphen, falithrom, phenpro and phenprogramma.

What other drugs are there?

Four new anticoagulants have been approved in recent years: apixaban, dabigatran, rivaroxaban and edoxaban. Like coumarins they are taken orally. Blood clotting monitoring is usually not necessary during treatment. But so far these new drugs have only been approved for the following: Prevention of stroke in people with atrial fibrillation and treatment or prevention of deep vein thrombosis in the legs and pulmonary embolism. Apixaban, dabigatran und rivaroxaban can be used for prevention of thromboses after fitting an artificial knee or hip.

There is not enough research on their use in pregnant or breastfeeding women, so women who are pregnant or breastfeeding should not take them.

There is another group of anticoagulants called heparins. These products have an immediate anti-clotting effect. That makes them especially suitable for acute treatment of venous thrombosis, pulmonary embolism and heart attacks as well as for prevention of venous thrombosis in people who have to have major surgery. Heparins have to be injected below the skin or into a vein to be effective. Because most patients who regularly have to take long-term medication prefer to take tablets rather than inject medication, heparins are generally not used for long-term treatment.

What are antiplatelets and how are they used?

Antiplatelets are weaker than anticoagulants, but side effects such as bleeding are also less common. They are mainly taken by people who have previously had a heart attack or stroke, in order to lower the risk of another attack. The most commonly used antiplatelet is aspirin (acetylsalicylic acid). Other antiplatelet drugs include clopidogrel, prasugrel and dipyridamole.

The type of anti-clotting medication that is prescribed will mainly depend on the person’s underlying medical condition. But age, other medical conditions and risk factors for bleeding also have to be considered. Intolerances of certain anti-clotting medications and possible interactions with other medications can also influence the choice. The advantages and disadvantages of the different anti-clotting medications have to be considered on an individual basis when deciding which treatment to use.

How do anticoagulants work?

Coumarins stop certain clotting factors that are produced in the liver using vitamin K from forming in the body. They do that by removing some of the vitamin K from the liver. That is why anticoagulants that work this way are sometimes also called vitamin K antagonists.

Coumarins only start to take full effect after two to four days once the clotting factors already in the blood have been broken down and the liver is no longer producing enough replacements.

Heparins directly and immediately inhibit certain clotting factors. That means that they already start to take effect after a few hours, making them especially suitable for acute treatment and short term prevention, for example after surgery.

The newer anticoagulants apixaban, dabigatran and rivaroxaban also immediately inhibit certain clotting factors. They also start to take effect after just a few hours. Overall, there is only limited experience with these newer anticoagulants.

How do antiplatelets work?

Antiplatelets inhibit the functions of blood platelets. They stop them from attaching to damaged blood vessels and sticking to each other, and therefore prevent blood clots from forming. That is why antiplatelets are also called platelet function inhibitors or platelet aggregation inhibitors (where aggregation means to stick together).

For many years now it has been known that ASA lowers the risk of blood clots. The older antiplatelet dipyridamole and the newer antiplatelets clopidogrel and prasugrel have a very similar effect to acetylsalicylic acid, even though they work in a slightly different way.

What possible side effects are there?

Anti-clotting medication should not stop blood from clotting completely. After all, if the blood did not clot at all injuries would lead to major blood loss. But if you are on anti-clotting medication, it does take longer for your body to close wounds and stop any bleeding. If you have a more serious injury, though, you might need synthetic clotting factors or vitamin K so that your blood clots faster.

Bleeding is the most common side effect of anticoagulant and antiplatelet medications. Light nose bleeds, gum bleeding or bruises on the skin are generally not a problem. But heavier bleeding has to be treated quickly. The following are signs that medical help is needed:

Heavy, persistent bleeding from the nose or gums

Large bruises

Red-colored urine

Blood in stool (dark red or black stool)

Blood in vomit

Strokes are a rare, but very severe side effect of anti-clotting medication. A very strong and sudden headache is a sign of such bleeding, especially if it occurs together with other problems like trouble seeing, dizziness, paralysis or numbness. If these kinds of symptoms occur, it is important to call an ambulance right away (112 in Germany).

Some anticoagulants can cause hair loss or rashes. In very rare cases clopidogrel and heparins can reduce the number of blood platelets to a dangerously low level.

One common way to make the use of anticoagulants safer is to have a medical ID card. They are available from doctors’ practices in Germany. It includes information about which illness the medication is taken for, what dosage needs to be taken and which doctor ought to be ed. In an emergency that information is then on hand immediately. This can help to prevent complications.

Can other medications influence the effect of anti-clotting medications?

People who take anti-clotting medication should pay attention to possible interactions with other medication. Some medications can increase or decrease the effect of anti-clotting medication, which can increase the risk of complications. That does not necessarily mean that no other medication can be taken at the same time as anti-clotting medication. But it does mean that extra monitoring might be needed. It is therefore a good idea to make a list of all medications you take and go through it with your doctor.

Interactions of coumarins

Coumarins have an especially high number of interactions with other substances, including with over-the-counter medications and herbal products. There are warnings of possible interactions with the following:

Antibiotics such as amoxicillin and ciprofloxacin

Psychotropic medication such as citalopram and sertraline

Medication taken against stomach ulcers such as cimetidine and omeprazol

Herbal products such as gingko, St John's wort and ginseng

Painkillers such as aspirin and paracetamol

Newer anticoagulants might have less interactions than coumarins. But because they have not been being used for as long there is less information available.

Interactions of antiplatelets

Aspirin is not only used as an antiplatelet but also in a higher dose as a painkiller. It can increase the risk of bleeding in the stomach. That is also true of other painkillers like diclofenac and ibuprofen. These medications can also limit the anti-clotting effect of aspirin. Paracetamol might be a better option for people who are already taking aspirin as an anti-clotting medication because it has no interactions with aspirin.

Can other factors such as diet influence the effect of coumarins?

There is no need to change your diet if you are taking coumarins. Because coumarins work by removing vitamin K from the liver, the vitamin K content of your diet has no influence. For example, there is a lot of vitamin K in foods like cauliflower, broccoli, beef and pork. Considerably changing what you eat, perhaps because you are on a diet, can have an effect on blood clotting.

Large amounts of alcohol can also influence the blood's ability to clot and intensify the effects of anti-clotting medication. But consuming moderate amounts of alcohol from time to time is not a problem. Acute and chronic gastro-intestinal tract conditions can affect the blood's ability to clot and the effects of the medication.

Physical activity and sports do not directly affect blood clotting. But if you take anti-clotting medication it is a good idea to make sure that the risk of injury and therefore of bleeding is not too high with certain sports.

If you change your eating habits and lifestyle or develop other illnesses, it is important that you have your blood coagulation levels checked more regularly. That way you can detect any changes early on and adjust the dose of your medication if necessary.

What should be kept in mind before surgery and other procedures?

If you are due to have major surgery it can be necessary to stop taking or adjust your anti-clotting medication a few days beforehand. Before having surgery or another procedure such as a gastroscopy you should make sure that the doctor knows if you are taking anti-clotting medication in advance. It can also be helpful to show them your medical ID card.

People do not always have to stop taking anti-clotting medication before smaller procedures and dental treatment. But it is better to find out ahead of time. That gives the doctor the chance to prepare in case any problems do occur during the treatment. It is also important that you make it known that you are taking anti-clotting medication before injections or vaccinations. This is because, for example, an injection into a muscle could cause more severe bleeding in the muscle.

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Updated November 26th 2014 November 26th 2014Created November 25th 2013Next update: 2017How we workPublished by the Institute for Quality and Efficiency in Health Care (IQWiG, Germany)About the institute